Senior Congress leader Pranab Mukherjee has said that his party will form an alliance with Trinamool Congress to fight the 2011 Assembly election in West Bengal. Brushing aside speculations of tension with ally Trinamool, he said, the two parties contested the last Lok Sabha elections together and will form an alliance for the Assembly polls too. Mr Mukherji was talking to reporters in Kolkata on Sunday. On December 20, Trinamool Congress leader Partho Chattopadhyay threatened to go it alone in the Assembly elections next year.